the theft won't "devalue" Bitcoins. even if the thief sells it's just another buying opportunity and might cause a temporary dip in the price. but that's assuming he wants to sell. he could be long term speculator like the rest of us hoping the price goes to $100 before he unloads. at the very least it will take him time to sell to get the right price and there's also the possibility mtgox intervenes once again. the only one's who will take a loss here are Zhou and possibly some of his customers.
But of course it will, doc, even if they buy the Bitcoins back at market! Hackers are not speculators, just think about every hack that has happened in Bitcoin’s history and the dumping that followed therafter (it is not as easy anymore since Gox collaborates to track stolen coins, but they just arbitrage it from a different exchange, and I suspect it is usually BTC-E.com). In addition, there is the breach of confidence that this currency is perhaps nothing but a collective subsidy to hackers.
